Sliding correlator techniques for spreading spectrum communication systems are employed to design a vector network analyzer. Cost and complexity of both the signal source and the receiver is much reduced. The measuring time can also be reduced and thus increases the efficiency of network measurements.
A vector network analyzer is an important instrument for measuring and characterizing RF or microwave devices and components. Most network analyzers currently sold on the markets adopt a super-heterodyne receiver architecture for measurements. Some calibration laboratory might use a six-port network analyzer in order to achieve measurement results with higher accuracy, nevertheless at the expense of much higher system complexity and cost. Another way to conduct network analysis is to use very high speed pulses and conduct measurements in time domain. But this method is still under development in some research laboratories.
Almost all the network analyzers currently sold on the markets adopt the super-heterodyne receiver architecture. FIG. 1 shows the example based on HP-8510 vector network analyzer. The analyzer uses two intermediate frequencies and four demodulation channels to detect the amplitude and the phase of the signal. This method requires signal source with high accuracy as well as a wide band scanning synthesizer, which increases the cost. In addition, frequency of the signal source should be able to vary either continuously or with very small increment in order to obtain continuous information in frequency domain. Measuring time can be very long when the target network is wide band in nature or when high resolution is required.
References to the application of sliding correlators are: R. J. C. Bultitude etc., in IEEE J. Selected Areas Cmmun., Vol. SAC-7 (I) p20-30 (1989) and Kaveh Pahlavan etc., in Wireless Information Networks, p114-120, John Wiley and Sons, inc. (1995).
The receiver architecture in the present invention is designed for spread spectrum communication, which is very different from the super-heterodyne receiver architecture widely used in the commercial vector network analyzer. Unlike the vector network analyzer based on the super-heterodyne architecture which uses narrow-band signal source, wide-band signal is introduced as the source in the present invention so that wide-band frequency response from the device under test can be gathered.
The present invention introduces the sliding correlator techniques which is commonly employed in spread spectrum communication systems. A sliding correlator technique is based on the time domain sliding effect caused by a small clock frequency offset in the pseudo random code generators of a transmitter and a receiver. A time scaled version of the impulse response of the device under test can be obtained from the time domain slided pseudo random code signals by a correlator. On the other hand, vector network analyzers based on the super-heterodyne receiver architecture uses the super-heterodyne technique to demodulate the transmitted signals. The high frequency signal feeding the device is down-converted to intermediate frequency region at the receiver so that the narrow-band response from the device under test can be demodulated. As a result, the information of each measurement in the present invention is much larger than the vector network analyzers based on the super-heterodyne receiver architecture.
The present invention uses only a synthesizer for frequency hopping unlike the continuous frequency scanning instrument in the super-heterodyne receiver architecture. For the same bandwidth, measurements can be done with several frequency hopping in the present invention instead of continuous frequency scan within the bandwidth. Therefore, the receiver in the present invention shows more simplicity.
This invention relates to a novel architecture of vector network analyzers for measuring and characterizing RF or microwave devices and components. Sliding correlator techniques are used in the design of vector network analyzers.
The target device is tested in the time domain, then the time domain response is converted into frequency domain by fast Fourier transform.
This invention also relates to a method for network measurements by these vector network analyzers.